1. Field of the Invention
The present invention relates to an endoscope system that images an oxygen saturation level of blood, a processor device of the endoscope system, and an image processing method.
2. Description Related to the Prior Art
In a medical field, an endoscope system is widely used for diagnosis and treatment. The endoscope system is constituted of a light source device, an endoscope device, a processor device, a monitor device, and an input device. In use of the endoscope system, an insert section of the endoscope device is introduced into a patient's body. An internal body portion is imaged by an image sensor provided at a distal end portion of the insert section, while being applied with illumination light from the distal end portion. There is also known an endoscope system that obtains various types of living body information from an image captured with the use of specific narrow band light as the illumination light.
According to US Patent Application Publication No. 2012/0157768 (corresponding to Japanese Patent Laid-Open Publication No. 2012-139482), for example, an endoscope system produces an oxygen saturation image (special image), which images an oxygen saturation level of blood, with the use of narrow band light having a wavelength range in which oxyhemoglobin and deoxyhemoglobin have different absorption coefficients as the illumination light. In this oxygen saturation image, a hyperoxic region having an oxygen saturation level of 60% or more is displayed with the same color as a normal image, which is obtained under irradiation with white light. A hypoxic region having an oxygen saturation level of less than 60% is displayed with artificial colors in accordance with the degree of the oxygen saturation level. Since the hypoxic region being a lesion-suspected portion and the hyperoxic region being a normal portion are colored differently, it is possible to grasp the distribution of a lesion at first sight.
Furthermore, this oxygen saturation image can indicate variations in the oxygen saturation level in the hypoxic region by difference in color among the artificial colors. On the other hand, the hyperoxic region is colorfully displayed just as with the normal image, and hence facilitates obtaining living body information useful for diagnosis, e.g. a blood vessel pattern and projections and depressions of a mucosal surface. Therefore, for the purpose of improving accuracy in diagnosis using the oxygen saturation image, it is demanded to increase visibility of living body tissue in the hyperoxic region and comprehensibility of the degree of the oxygen saturation level in the hypoxic region.